package ${initProjectVo.packageNameValue}.common.lang;

/**
* @author Faye.Wang
* @version 1.0
* @date 2020/11/3 17:54
* @Description
*/

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.Enumeration;

/**
* id自增器（雪花算法）
*
* @author renjie
* @version 1.0.0
*/
public class SnowFlake {
private final static long twepoch = 12888349746579L;
// 机器标识位数
private final static long workerIdBits = 5L;
// 数据中心标识位数
private final static long datacenterIdBits = 5L;

// 毫秒内自增位数
private final static long sequenceBits = 12L;
// 机器ID偏左移12位
private final static long workerIdShift = sequenceBits;
// 数据中心ID左移17位
private final static long datacenterIdShift = sequenceBits + workerIdBits;
// 时间毫秒左移22位
private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
//sequence掩码，确保sequnce不会超出上限
private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
//上次时间戳
private static long lastTimestamp = -1L;
//序列
private long sequence = 0L;
//服务器ID
private long workerId = 1L;
private static long workerMask = -1L ^ (-1L << workerIdBits);
//进程编码
private long processId = 1L;
private static long processMask = -1L ^ (-1L << datacenterIdBits);

private static SnowFlake snowFlake = null;

    static{
        snowFlake = new SnowFlake();
    }
    public static synchronized long nextId(){
        return snowFlake.getNextId();
    }

    private SnowFlake() {
        //获取机器编码
        this.workerId=this.getMachineNum();
        //获取进程编码
        RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
        this.processId=Long.valueOf(runtimeMXBean.getName().split("@")[0]).longValue();

        //避免编码超出最大值
        this.workerId=workerId & workerMask;
        this.processId=processId & processMask;
    }

    public synchronized long getNextId() {
    //获取时间戳
    long timestamp = timeGen();
    //如果时间戳小于上次时间戳则报错
    if (timestamp < lastTimestamp) {
        try {
            throw new Exception("Clock moved backwards.  Refusing to generate id for " + (lastTimestamp - timestamp) + " milliseconds");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    //如果时间戳与上次时间戳相同
    if (lastTimestamp == timestamp) {
        // 当前毫秒内，则+1，与sequenceMask确保sequence不会超出上限
        sequence = (sequence + 1) & sequenceMask;
        if (sequence == 0) {
            // 当前毫秒内计数满了，则等待下一秒
            timestamp = tilNextMillis(lastTimestamp);
        }
    } else {
        sequence = 0;
    }
        lastTimestamp = timestamp;
        // ID偏移组合生成最终的ID，并返回ID
        long nextId = ((timestamp - twepoch) << timestampLeftShift) | (processId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    return nextId;
    }

    /**
    * 再次获取时间戳直到获取的时间戳与现有的不同
    * @param lastTimestamp
    * @return 下一个时间戳
    */
    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }

    /**
    * 获取机器编码
    * @return
    */
    private long getMachineNum(){
        long machinePiece;
        StringBuilder sb = new StringBuilder();
        Enumeration<NetworkInterface> e = null;
    try {
        e = NetworkInterface.getNetworkInterfaces();
    } catch (SocketException e1) {
            e1.printStackTrace();
    }
        while (e.hasMoreElements()) {
            NetworkInterface ni = e.nextElement();
            sb.append(ni.toString());
        }
        machinePiece = sb.toString().hashCode();
        return machinePiece;
    }
}